It is known that a latent electrostatic image can be developed with toner particles dispersed in an insulating nonpolar liquid. Such dispersed materials are known as liquid toners or liquid developers. A latent electrostatic image may be produced by providing a photoconductive layer with a uniform electrostatic charge and subsequently discharging the electrostatic charge by exposing it to a modulated beam of radiant energy. Other methods are known for forming latent electrostatic images. For example, one method is providing a carrier with a dielectric surface and transferring a preformed electrostatic charge to the surface. Useful liquid toners comprise a thermoplastic resin and dispersant nonpolar liquid. Generally a suitable colorant is present such as a dye or pigment. The colored toner particles are dispersed in the nonpolar liquid which generally has a high-volume resistivity in excess of 10.sup.9 ohm centimeters, a low dielectric constant below 3.0 and a high vapor pressure. The toner particles are less than 10 .mu.m average by area size. After the latent electrostatic image has been formed, the image is developed by the colored toner particles dispersed in said dispersant nonpolar liquid and the image may subsequently be transferred to a carrier sheet.
In one method of preparation of liquid toners for electrostatic imaging, the plasticizing of the thermoplastic polymer and colorant, if present, with a dispersant nonpolar liquid forms a gel or solid mass which is shredded into pieces, more nonpolar liquid is added, the pieces are wet-ground into particles, and grinding is continued which is believed to pull the particles apart to form fibers integrally extending therefrom. While this process is useful in preparing liquid toners, it requires long cycle times and excessive material handling, i.e., several pieces of equipment are used.
In another method of preparation of toner particles, the plasticizing and liquifying of a thermoplastic resin, a dispersant nonpolar liquid having a Kauri-butanol value of less than 30, and optionally a colorant to form a dispersion of toner particles is accomplished in a vessel in the presence of moving particulate media, the temperature being maintained to plasticize and liquify the resin but below that at which the dispersant nonpolar liquid degrades or boils and any component decomposes. The dispersion is then cooled to permit precipitation of the resin out of the dispersant, the particulate media being maintained in continuous movement during and subsequent to cooling whereby no gel or solid mass is formed and the toner particles having an average by area particle size of less than 10 .mu.m are formed. The particulate media is then separated from the dispersion of toner particles. While this process, which requires a single piece of equipment, is useful in preparing the toner particles. particularly those having a plurality of fibers integrally extending therefrom, it requires long grinding times to attain the specified particle size.
It has been found that the above disadvantages can be overcome and toner particles prepared by a process that may not require excessive handling whereby toner particles are dispersed and toner particles are formed having an average size by area below 10 .mu.m in the same vessel. The grinding time is reduced up to 20% over the process using a single piece of grinding equipment without a polar additive present.